Electrodeposition of chromium



Patented Aug. 3, 1937 UNITED STATES PATENT OFFICE Y rialNmMZJZS. In

1 Claim.

It has been proposed to electroplate' or depoflt chromium from asolution of a chromic salt, but this has heretofore been imposible. Ifinsoluble anodes are used, products are formed which de- 5 stroy thedepomt of chromium. I! chromium anodes are used, the chromium dissolvesas chromlc acid and not as a chromic salt, so that deposition takesplace from a chromic acid so- N lution and not from a chromium saltsolution.

An object of mypresent invention is o provide a process in whichchromium dissoives at the anode as a chromium salt and not as chromicacid. In my present invention the solution of chromium from a chromiumanode as a chromium J salt, and not as chromic acid, is achieved byadding to the electrolytic bath, comprising for example a chromiumsolution, which form special compounds with the chorimum and which donot, therefore, produce the well known ionic reactions of chromium. Thatis, they form compounds in which the chromium enters as a part of thecomplex ion and not as chromium ion or chromic acid ion.

Such substances that may be added are sulphites, thiocyanates orsuliocyanates and the like. Any suitable salt containing the desiredanion, for example an alkali thlocyanate such as ammonium thiocyanate,potassium or sodium 30 thiocyanate, or alkaline earth thiocyanates orthiocyanates of other metals'can be employed.

June 29, 19

(CI. I'M-l) 260 gr. of chromic chloride crystals 50 er. of ammoniumchloride 40 gr. of ammonium thiocyanate to gr. of boric acid 1 liter oi.water Temperature of bath: 20 C. Current density: 800 to 1000 amp./mVoltage: 4.6-5.8 volt From this solution a lustrous chromium deposit isobtained. It the thiocyanate or ammonium content is increased, black,glossy, firmly adhering deposits are obtained.

What I claim is:

A process for the electrolytic deposition of chromium which comprisespassing an electric current from a chromium anode to a cathode throughan aqueous solution containing complex ions of chromium and thiocyanateradicals whereby chromium dimlves from said anode to form said complexions and is deposited at said cathode.

